Mobile is quickly becoming the new normal for YouTube, and it’s
starting to pay off: 40 percent of all of the service’s video views in
the U.S. are now coming from mobile devices, a YouTube spokesperson told
GigaOM on Wednesday. Worldwide, mobile is now responsible for 25
percent of all of YouTube’s video views.

This, and the roll-out of new mobile apps, has helped YouTube to triple its mobile ad revenue in the past six months, according to Bloomberg, which got YouTube VP of Sales Lucas Watson go on the record about the mobile growth.